Award: OCE-1657727

Biogeochemical processes can be estimated by the exchange of vital tracers between the seafloor, overlying water, and the atmosphere and are paramount to understanding global biogeochemical cycling. Techniques that measure water transport and tracers of these processes (here oxygen and pH) have revolutionized how these exchanges are studied, and how they impact local water quality, productivity, and nutrient cycling. Through measurements of oxygen concentration and pH, and their transport by water movement, their exchange can be determined. This project used the newly developed eddy covariance hydrogen ion and oxygen exchange systems (ECHOES) to evaluate the coupled benthic processes of photosynthesis / respiration and dissolution / calcification at an ecosystem scale on the Bermuda platform and in the Florida Keys, to quantify their contribution to carbon cycling, water column chemistry and the effects of adjacent benthic communities. The co-measured hydrogen ion (or pH) and oxygen exchange rates (in combination with discrete measurements of carbonate chemistry) provided a comprehensive analysis of the total ecosystem carbon cycling and allowed for a truly in situ examination of the natural drivers of carbon cycling, metabolism, and calcification. These results revealed interactions between these processes through high frequency, ecosystem scale measurements that are now possible with the ECHOES. The influence of benthic processes on shallow coastal waters highlighted the multiple parameter dependency (residence time, benthic community, light) of the local carbonate chemistry and the potential resilience of dynamic coastal environments to changing ocean conditions. Eddy Covariance techniques were originally developed to examine exchange between the land and atmosphere (e.g. carbon dioxide flux towers, or eddy covariance flux towers), but applying these techniques to aquatic ecosystems presented challenges due to surface waves that were present in the shallow aquatic ecosystems where these aquatic techniques are commonly applied. Waves caused errors in the sensors used to measure water transport and tracer concentrations, and presented significant challenges for applying these atmospheric techniques underwater. This research developed new guidelines for these aquatic exchange measurements that required a change in how measurements were conducted and analyzed, to allow for tracer exchange measurements in the presence of waves. These new guidelines also now allow for new sensors that were previously incompatible, expanding the applications of the eddy covariance technique to new scientific research questions. Last Modified: 06/16/2021 Submitted by: Matthew Long